1. Field of the Invention
The present invention relates to the field of microbiological technologies, and more particularly, relates to a cadmium-removing bacterium Lactobacillus plantarum strain and the use of the same.
2. Description of the Related Art
Cadmium is a heavy metal that is extremely harmful to human health, which is very stable in the environment and easy to be accumulated in the body. Metal cadmium can react with oxygen, chlorine, sulfur and other elements to form inorganic compounds and exist in nature in the form of compounds. Most cadmium salts are soluble in water. Nowadays, cadmium is widely used in electroplating, cadmium-nickel batteries, alloys, pigments and plastics, etc. With the increase of its applications in industry and human daily life, cadmium content in water and soil is increased every year. As a result, cadmium has been accumulated in plants and animals (e.g. cadmium contaminated rice, tobacco, sea food, and animal organs), and eventually became accumulated in human beings through the food chain. Cadmium contamination is particularly serious in some Asian countries. In 1995, the outbreak of “Itai-Itai” disease in Japan, which shocked the world, was caused by cadmium contamination in Jinzu River, resulting in highly contaminated rice that were consumed by local residents. In China, cadmium has become one of the most serious environmental pollutants to land and water with the discharge of about 680 tons of cadmium-containing industrial waste every year. It has been reported that the area of arable lands contaminated by cadmium has reached 8000 acres in China and the cadmium content in the rice fields even reaches 25 times more than that of the allowable national limits in some heavily contaminated areas. In 2002, the Ministry of Agriculture conducted a national wide inspection of the rice market and found that 10% of the rice on the market contains levels of cadmium more than that of the national standard. In 2007, professor Gengxing Pan from Nanjing Agriculture University and his research team conducted another inspection of the rice cadmium content in six districts of the country (district of Eastern China, Northeast China, Central China, Southwest China, South China, and North China), and found similar results. Cadmium is highly toxic and has a long incubation period. The Agency for Toxic Substances and Disease Registry (ATSDR) and the United States Environmental Protection Agency (EPA) have been listing Cadmium as the sixth most toxic substance to human health that can cause damage to bone, kidney, liver, respiratory system, circulation system, and reproductive organs. In addition, cadmium can cause cancer. The International Union Against Cancer listed cadmium as an IA level carcinogen in 1993. Acute cadmium poisoning causes coughing, stuffiness, dyspnea, nausea, vomiting, abdominal pain and other symptoms. Large doses of cadmium intake can even result in death due to acute liver damage. Chronic cadmium poisoning can lead to kidney damage (e.g. proteinuria, kidney stones, and chronic renal failure), bone damage (e.g. bone pain, osteoporosis, osteomalacia, and spontaneous fractures), damage to the reproductive organs (e.g. testes and ovaries damage) and cancer (e.g. lung cancer and prostate cancer). Half-life of cadmium in human body is as long as 10-30 years, which makes cadmium poisoning easily overlooked.
The most common way to treat the physiological disorders caused by cadmium poisoning is to promote cadmium excretion by chelation (e.g. EDTANa2Ca, Sodium dimeraptosuccinate (DMSA)) therapies. For example, Chinese Pharmacopoeia, Second Edition (2000) documented using edetate calcium disodium as antidote for heavy metals poisoning caused by cadmium and lead. However, all of these drugs have side effects to some degree. EDTANa2Ca is a broad spectrum chelator with a strong renal toxicity. A large number of essential trace elements such as zinc, copper, manganese and iron, which are important for enzyme activities, will be excreted out of human body through urine when using EDTANa2Ca as a chelator. Therefore extensive uses of calcium disodium edetate can cause damages to human health. DMSA is effective only if given within a short period of time after cadmium exposure and can cause headache, nausea, limb pain and digestive system disorders (Kojima, S., Sugimura, et. al. Effects of dithiocarbamates on testicular toxicity in rats caused by acute exposure to cadmium. Toxicology and applied pharmacology, 116, 24-29, 1992).
Because of some side effects of traditional treatments against cadmium poisoning, there is a need in looking for new intervention or therapeutic methods. Lactic acid bacteria (LAB) is a general name for bacteria that can convert carbohydrates to lactic acid. LAB widely exist in natural fermented dairy products, fermented vegetable foods such as pickles, sauerkraut, silage, and human intestine. Long term studies have showed that some LAB strains are beneficial probiotics that play important roles in human health, for example, preventing lactose intolerance, adjusting the microecological balance, preventing cancer, controlling toxin levels in body, protecting the liver and enhancing its detoxification capability. Furthermore, it has been reported that as a food grade microorganism, LAB can bind and remove heavy metals such as cadmium and lead in vitro (Halttunen, T., Collado, M. C., et. al. Combining strains of lactic acid bacteria may reduce their toxin and heavy metal removal efficiency from aqueous solution. Letters in Applied Microbiology, 46, 160-165, 2007). Therefore, LAB have a great potential to become new healthy foods with cadmium-removing capability.
Currently, a number of patent documents have disclosed methods for preparing healthy foods against cadmium poisoning. Chinese patent CN1336208 discloses a healthy food made of deodorized garlic powder, vinegar powder and “Bing Ming powder” (a mixture of borneol powder and alum powder), which can help excrete cadmium accumulated in human body due to exposure to contaminated air, water, or pesticides. Chinese patent CN1328845 discloses one Chinese medicine made of smilax, red ginseng, panax and some other materials that can effectively function to prevent and treat cadmium poisoning without side effects. However, there are few patents related to cadmium-removing bacteria. Chinese patent CN101153272 discloses that Burkholderia yabunchi J62 has a good tolerance to cadmium and it can be used in the field of environmental engineering to promote plant growth, help plants accumulating cadmium and improve soil quality. Chinese patent CN101252943A discloses a Lactobacillus plantarum that can help mammal to absorb iron, zinc, calcium and magnesium ions.
In summary, there is a need in isolating LAB strains having good cadmium tolerance and absorption capacity, proving their cadmium-removing ability in animal models, and developing cadmium-removing LAB products. It is the goal of the present invention to explore novel beneficial features of probiotics, isolate lactic acid bacteria with high health values, and develop a new dietary therapeutic strategy against cadmium poisoning.